In a passenger aircraft (hereinafter referred to as “aircraft”), passengers board or disembark from (hereinafter referred to as “board and the like”) the aircraft through a doorway provided to an airframe. Between the doorway and a gate provided in the airport building, a PBB is installed. Normally, the PBB is stored in a contracted state when no passengers and the like are boarding. At the time of boarding and the like of the passengers on the aircraft, the PBB extends toward the doorway of the aircraft to connect to the doorway of the aircraft. The PBB is fixed after being substantially matched with the doorway of the aircraft, to thereby enable the passengers and the like to board and the like through the doorway.
The PBB generally includes an inner tunnel (first tunnel) and an outer tunnel (second tunnel). The inner tunnel and the outer tunnel are each a hollow member through which the passengers are walkable, and are configured so that the outer tunnel has an outer shape larger than the cross section of the inner tunnel, and the inner tunnel is telescopically inserted into the outer tunnel from one end side thereof. The outer tunnel is supported by a drive column, and the drive column includes a wheel for moving on the ground. Through running of the drive column, the outer tunnel is moved to relatively approach the inner tunnel and overlap with the inner tunnel, thereby contracting the PBB. On the other hand, when the outer tunnel is moved to relatively separate from the inner tunnel, the PBB extends. The inner tunnel is connected to the airport building through intermediation of a rotunda. On the other hand, a cab is arranged on an end portion of the outer tunnel on a side opposite to one end at which the inner tunnel is inserted, that is, the other end side (aircraft side) of the outer tunnel. An end portion of the cab, which is situated on the side opposite to the side on which the outer tunnel is connected, is connected to the doorway of the aircraft.
The PBB has a structure in which the inner tunnel is inserted into the outer tunnel having a larger outer shape in cross section. Therefore, there has been a problem in that, at a joint part between the outer tunnel and the inner tunnel, a level difference is generated in the passage floor surface on which the passengers and the like walk. Such a level difference in the floor surface is dangerous because the passengers may fall during walking. Further, the level difference causes great inconvenience in running by a wheelchair or conveyance of a wheeled baggage. As a PBB that eliminates such a passage level difference inside the PBB, for example, Patent Literatures 1 to 3 below disclose a PBB including a continuous floor that is mountable and fixable to the inner tunnel. In particular, in Patent Literature 1 as a representative example thereof, for example, a sprocket is arranged on the lower side of the inner tunnel. The mechanism is as follows. When the inner tunnel and the outer tunnel move relatively to each other to contract the PBB, a floor surface of the passage of the outer tunnel approaches the inner tunnel. Therefore, a floor surface fixed to the inner tunnel is guided by the sprocket toward the opposite direction to be wound by a rope retractor to be shortened.